A network device according to the opening paragraph may be used in a sensor network. Sensor networks require a common notion of time among the network devices. In ‘Time Synchronization in Sensor Networks: A survey’, by Fikret Sivrikaya et, al., IEEE Network, July/August 2004, time synchronization in wireless networks such as sensor networks is discussed. Time synchronization in a network aims to provide a common timescale for local clocks of the network devices comprised in the network. A common notion of time is for example needed to be able to correlate measurement data taken by multiple network devices. To enable a correlation of the measurements each measurement is given a timestamp reflecting the time at which the measurement was done. This induces a need for synchronization of the clocks of the network devices.
Commonly network time synchronization methods rely on some sort of message exchange between network devices. Such a message may comprise a timestamp including a clock value of a sending network device. On receiving said message a receiving network device may compare its clock value with the received timestamp included in the message and synchronize its clock. However the local clock of the receiving network device may drift away from time to time from the local clock of the sending network device causing a recurring need to synchronize said local clocks.
In a wireless network the network device may have a limited energy source such as a battery. Each clock synchronization requires the exchange of time stamps and a sequence of calculations, and thus each synchronization causes energy consumption.
It is therefore a problem that while the available energy source of the network device may be limited the calculations involved in the time synchronization between network devices contribute to the energy consumption and a reduction of battery life.